1. Field of the Invention
The present invention relates to imaging devices, cameras, and imaging methods.
2. Description of the Related Art
One of the known techniques for taking a single image with a wide dynamic range by multiple exposure is discussed in, for example, Japanese Patent Laid-Open No. 7-298142 (Patent Document 1; corresponding to U.S. Pat. No. 6,480,226). This publication proposes the idea of taking two images under different exposure conditions, one for highlight regions and the other for shadow regions.
Japanese Patent Laid-Open No. 2002-135648 (Patent Document 2; corresponding to US AA2003095192 (publication)), which references Patent Document 1, discusses the idea of determining suitable exposure conditions for highlight regions and shadow regions using a device configured to obtain pre-imaging information. The suitable exposure conditions can be determined before main imaging by obtaining information on a subject and finding peaks corresponding to highlight regions and shadow regions in a brightness histogram.
Another idea is discussed in Brian A. Wandell, Peter Catrysse, Jeffrey M. DiCarlo, David Yang, and Abbas El Gamal, “Multiple Capture Single Image with a CMOS Sensor”, Chiba Conference on Multispectral Imaging, pgs. 11-17, 1999 (Non-Patent Document 1). This idea is to take four images, for example, with amounts of exposure varying in increments of two exposure steps.
The ideas described above have several problems in determining predetermined exposure conditions with a multiple-exposure imaging device.
Patent Document 1 discusses no specific device configured to set exposure conditions suitable for highlight regions and shadow regions.
Patent Document 2 discusses the setting of exposure conditions suitable for peaks in a brightness histogram, although the document does not discuss how to deal with the case where the number of the peaks exceeds the number of images taken in multiple exposure and the case where only one peak appears. The idea discussed in Patent Document 2 thus collapses completely in such cases. In addition, examples of the shapes of histograms shown in embodiments of Patent Document 2 can be difficult to implement practically.
Furthermore, the idea discussed in Patent Document 2 discusses the input of pre-imaging information before main imaging. For motion video applications, for example, the idea has difficulty in achieving high frame rates because the idea involves pre-imaging and the accompanying signal processing for every frame using some device.
According to Non-Patent Document 1, exposure conditions are varied in increments of the same number of exposure steps at all times. This idea leaves room for improvement because it overlooks the brightness distribution of a subject to be imaged and thus can fail to achieve suitable exposure.